Process of treating light oils produced in by-product coking of bituminous coal in order to obtain a water-soluble acid sludge



Patented May 22, 1945 PROCESS OF TREATING LIGHT: OILS. PRO- DUCE'II IN BY-PR'ODUGT: COKING. ()F BI; TUMIN'OUS" COAL' IN ORDER TO' OBTAIN A WATER-SOLUBLE" ACID SLUDGE Joseph H. Wells and Philip 1; Wilson, J12, .Pittse burgh,gPa., assignors to Carncgieell'linois Steell Corporation, alcorporation oi.- New Jersey,

No Drawing: Application January 2; 194a, SerialNo. 411,212

8 Claims.

Inby-product coke works; a considerable prob lem arises in the disposal of acid sludge which results-from the washing of light-oils: The-disposal of such material without contaminating the atmosphere orpolluting a stream; or otherwise creating a menace-to public health; constitutes a large and dfificult problem.

The light oil which is recovered' from" the gas-- produced in a lb'y-product coke" plant' consists principally of benzene, toluene; and xylene-w Manyother compounds are present ir-rless amounts and they must be separated from the benzene and 9 its homologs in order to obtain a marketablerbenzene' and the like;

An important group or suchcompoundswhich must be thus" removed are sulphur=containing organic compounds, of which group carbon di sulphide and thiophene arerepresentative compounds:

Another group or compounds which must be removed includes unsaturated compounds including diencs and oleiins. Pentenes, cyclopentae diene; styrene; anchindene are representative of this;group".

Still other classes oi compounds are present as well, but the sulphur-containing; compounds and. the unsaturated compounds are thetwomost' important impurities: Although some of these compounds are separated for sale; with respect to the pure benzene and its homologs; they must be -considered as'impurities:

Of the impurities, one totwo per cent, based on the'volume of the light oil, distill-lbelow 80 0., tlie*bl1ing-p0int-of benzene: of theseiorerunnin'gs can be separated from the bull c-of-the light oilbv fractional distillation. Ih' thi-sfraction of the light oil are found" cyclo pentadiene and carbon disulphide;

ilarge proportion- Another'portion of thelight oil distills' above" 145 C. the boi-lingpointof ortho xylene, and" likewisecan he separated to a large extentbl fractionaldistillation. In this-=fraction will be foundcumarone, mesitylene, indene; and-naphthalene:

The iorerunningsand the high-boiling fractiori of the light oil do not include-"all l ofthe im-puri ties; a certain"proportion"distills between 0'.

and--"-C'.- The impurities=boiling"inthis temperature range cannot be separated-hi"fractional distillation, butcan 'be removed by" treating the lightoil with sulphuric acid. Theacidreacts with" Some com pounds it will polymerizetohigh molecular resins or p itches; others'will sulphonate; and still others areoxidized; The reactions are extremely com theimpuritiesindifferent wayss is first fractionated crudely totake out the highest boilingcompounds. Insome cases this fractionation may inc-lude removal-of forerun ningsboiling helow 80- C.

The distilled. light oil then is washed with concentrated sulphuricacid-in a large vertical; cylindrical tank equipped'witlr amixing device; Several percent byzvohime of the acid arerun into the oil. in'theemixing tanlr' or agitator; The two' are mixed atsubstanti'ally room temperature until i the reaction 1 between 1 acid andimpurities has proceededsuuihcientlyfar to" insure theirremoval frointheoil, Onsetthng, a heavy layer,

which consists of um-used acid 'andcomplex prodnets of the reaction, collects in the bottom of theag-itator; This --layer"is" sticky'- and viscous with a brownish red or p'urpleccolor and axstrong' odor of sulphur dioxide.

This acid. sludge is di fiicult of disposal; For" ones-reason, its-highacid content renders-it corrosivea to equipmentin which it is handled. If the sludge is burned, the sulphur from its organic matter: and excess acid *isevolved 'as sul-phur dioxide and sulphur tri'oxide which may pollute: tneatmospherevery seriously." If thrown on dump the high" content of" organic matter makes the sludge a-ih-e= hazard; In addition; the dump. must he fenced oil" carefully so that human be ings and animals will beunable to get into itby" accident.

A great deal of studY- has-been devoted to findmg some processwh-ichwill improve the quality" of this -s1u'dge-,- a-better method-for its-disposal, or" some use for it.- The sludge-still contains a largeproportion of the original sulphuric 'acid-wl1ichhas not reactedu Several methods are used for re: covery 1 of this acid;

Oneof thesemethods isto'boil thesludge with steam. During the-(boiling, the=sludge separates into two'laye-rs; one-a; mass of pitch and the othei" d lute, but impure acid. The latter'usuallyfcan b'c used aroun'd' the plan t, but the-;disp'osa1 oi thepitch still is at-problem; This process does have": the advantage; however, that the-volumeof' the" sludge to' be disposed cfisreducedj Another method for recovery oi the" acid is'to I dilute acid y the agitators afterthe agitation is continued. When the acid phase and the water have been properly contacted, the agitator is stopped, and the contents of the vessel are allowed to'settle. Three separate layers form in the agitator. At the bottom is a layer of diluted acid, relatively low in organic matter,

' which acid is referred to as spent acid. Above this is a viscous layer of polymerized and reacted organic matter which still contains some acid and some oil, possibly both in solution and entrained. In the subsequent discussion, this will be termed the acid sludge. On top is the washed light oil.

The acid sludge and spent acid are drawn ofi together from the agitator into a lead lined tank and there are boiled with direct steam. The steam vaporizes any light oil present, and the latter distills oh and is condensed. It also polymerizes and causes further reaction of the organic matter. When boiling has been completed, this polymerized organic matter in the form of a black pitch rises to the top of the dilute acid solution in the tank. The acid can b drawn off for further use, but the pitch like the other acid sludges is difficult of disposal. The content of the spent acid is reduced by the boiling.

Th two processes described above do reduce the volume of the acid sludge and serve to recover much of it as dilute acid which may be utilized in other processes. However, in both cases, a large amount of acid pitch is left, the disposal of which is still a problem.

In accordance with the present invention, there is provided a further improved process, by means of which process the acid sludge referred to above, can be recovered as a neutral, aqueous solution which is handled more easily and can be treated more readily for the recovery of values.

The process of the present invention consists of the following steps:

1. The oil is fractionated carefully to remove as much of the impurities boiling below 80 C. as possible. Their separation is made substan tially complete by distilling off -20 per cent of the benzene present in the oil as a second fraction which may be utilized in other than pure products.

The distillation is continued and a third fraction of the light oil is collected. This contains the balance of th benzene, the toluene, and the xylene, all of which are to be washed with sulphuric acid. In order to recover the Xylene completely, the end point of this fraction may be carried up to between 150 and 160 C. or even a little higher.

2. The crude benzene, toluene and xylene fraction is washed with sulphuric acid in the customary manner. After the acid washing is complete, water is added to the agitator, as has been described above in the second acid recovery process. After settling both spent acid and acid sludge are drawn 01f together intoa separator. Here they settle further and the spent acid on the bottom is finally pumped to a third tank. The acid sludge remains in the separator.

3. Ammonia now is added to the acid sludge in the separator, either in the form of a gas or as a more or less concentrated solution of ammonium hydroxide. Mixing is desirable in order to neutralize the sludge uniformly. If the spent acid has been separated carefully from the sludge, the temperature of the system should not rise higher than 70-80 C., but if it approaches the boiling point, admission of ammonia should be stopped and the system cooled.

4. The acid sludge now is in the form of a thin, clear, brown solution, neutral or slightly alkaline with ammonia. Any light oil which the sludge has contained separates as a layer on the surface. The sludge solution can be drained to a, storage tank. The water content of this solution will vary because it depends largely on the water content of the neutralizing ammonia. Since the sludge always contains some Water, water for solution will be present in case substantially dry ammonia gas is used for neutralization.

The following steps represent an alternative procedure which offers certain advantages over the above, while embodying the principal reactions set forth above:

1. The crude light oil described above.

The fractionated oil is washed with acid as in the above method, but only the spent acid is drained from the washer. The acid sludge is left in the oil.

3. Ammonium hydroxide solution is added to the agitator in sufficient volume to neutralize both the acid sludge and the light oil. When neutralization is complete, the solution of acid sludge is settled out and drawn from the washed light oil. This process has the further advantage that the light oil and the acid sludge are neutralized b the same operation. I

If desired, other alkalis such as sodium hydroxide or a sodium carbonate may be used instead of ammonia, and, less preferably, lime or magnesia. These last two reactants, however, precipitate insoluble compounds.

The improved process is illustrated by the following illustrative example:

Ten-thousand gallons of light oil were fractionated. The following fractions were collected:

1. gallons of forerunnings, which distilled up to 75 C.

2. 1,000 gallons of crude benzene which contained substantially all forerunnings not separated in the previous fraction.

3. 7,500 gallons of benzene, toluene and xylene distilling up to an end point of C.

4 1,350 gallons of residue left in the still which may be, fractionated further if desired.

is fractionated as The 7,500 gallons of benzene, toluene and xylene were washed with 55 gallons of 66 Be. sulphuric acid for 30 minutes.

After settling for 15 to 30 minutes, the resulting acid sludge was drawn off to the boiling tank. gallons of 66 B. sulphuric acid then were added to the oil, and the two were agitated in contact for one to three hours. From 200 to 400 gallons of water were added, and the agitator was allowed to settle for from 30 minutes to an hour, and both spent acid and acid sludge were drained into the boiling tank containing the previous acid sludge. Both sludges were mixed by stirring for 20 minutes until the dilute acid from the second wash caused a separation of the spent acid and sludge from the first wash. The spent acid solution now was pumped to another tank in which it was boiled with direct steam to separate small amounts of organic matter still dissolved or entrained.

To the acid sludge left in the boiling tank were added 95 gallons of a 20% solution of ammonia, the acid sludge being mixed continuously during admission of the ammonia until neutralization was complete. 142.5 pounds of ammonia were required. The contents of the tank were allowed to settle and 300 gallons of clear brown solution containing about 25 per cent water were drawn off. 20 gallons of oil were left in the tank and returned to another batch of light oil being washed with acid in the agitator.

The solution produced from the sludge by the above-described procedure is suitable for ready disposal in any convenient manner.

We claim:

1. The process of treating light oils produced in the production of coke from bituminous coal, which comprises fractionating light oil to remove at least the major portion of impurities boiling below 80 0., completing the separation of such impurities bydistilling 01f from approximately per cent to approximately '20 per cent of benzene present in the oil, thereby forming a second fraction, continuing the fractionation of the light oil to produce a third fraction containing the balance of the benzene, together with the toluene and xylene contained in the original light oil, washing this third benzene-toluene-xylene fraction with sulphuric acid, adding water to the resulting washed mixture, withdrawing spent dilute acid from the resulting material, neutralizing the resulting acid sludge with a neutralizing agent selectedfrom the group consisting of alkali hydroxides and alkali carbonates, and separating the resulting neutralized acid sludge as a thin clear solution' from the said benzene-toluenexylene fraction.

2. In a process of treating light oils produced in by-product coking of bituminous coal in order to obtain a water-soluble acid sludge, wherein the light oil is fractionated to remove at least the major portion of impurities boiling below 80 C., the separation of such impurities being completed by distilling off from approximately 10 per cent to approximately per cent of benzene present in the oil, thereby forming a second fraction, the fractionation being continued to produce a third fraction containing the balance of the benzene together with the toluene and xylene contained in the original light oil, the improvement which comprises obtaining an acid sludge capable of forming a thin, clear, aqueous solu tion, by washing the said third benzene-toluenexylene fraction with sulphuric acid, adding water to the resulting mixture, allowing spent dilute acid and resulting acid sludge to settle into layers, removing the spent dilute acid and acid sludge from the washed benzene-toluene-xylene fraction, allowing the removed spent dilute acid and acid sludge to separate into layers, separating the resulting layers of spent dilute acid and acid sludge, and neutralizing the acid sludge with a neutralizing agent selected from the group consisting of alkali hydroxides and alkali carbonates,

thereby converting the said acid sludge into a thin, clear aqueous solution suitable for disposal.

3. The process of treating light oils produced in the production of coke from bituminous coal which comprises fractionating light oil to remove at least the major portion of impurities boiling below 80 C., completing the separation of such impurities by distilling off from approximately 10 per cent to approximately 20 per cent of benzene present in the oil, thereby forming a second fraction, continuing the fractionation of the light oil to produce a third fraction containing the balance of the benzene, together with toluene and xylene contained in the original light oil, washing this third benzene-toluene-xylene fraction with sulphuric acid, adding water to the resulting washed mixture, withdrawing spent dilute acid from the resulting material, neutralizing the resulting acid sludge with ammonium hydroxide and separating the resulting neutralized acid sludge as a thin clear solution fromthe said benzene-toluene-xylene fraction.

4. The process of treating light oils produced in the production of coke from bituminous coal as claimed in claim 1, wherein the acid sludge is neutralized with caustic soda, and the resulting neutralized sludge is withdrawn as a thin clear solution from the benzene-toluene-xylene fraction.

5. The process of treating light oils produced in the coking of bituminous coal as claimed in claim 1, wherein the acid sludge is neutralized with sodium carbonate and the resulting neutralized sludge is withdrawn as a thin clear solution from the benzene-toluene-xylene fraction.

6. In a process of treating light oils produced in by-product coking of bituminous coal in order to obtain a water-soluble acid sludge as claimed in claim 2, the step of neutralizing the acid sludge with ammonium hydroxide, thereby converting the said acid sludge into a thin, clear aqueous solution suitable for disposal.

7. In a process of treating light oils produced in by-product coking of bituminous coal in order to obtain a water-soluble acid sludge as claimed in claim 2, the step of neutralizing the said acid sludge with sodium hydroxide, thereby converting the said sludge into a thin, clear aqueous solution suitable for disposal.

8. In a process of treating light oils produced in by-product coking of bituminous coal in order to obtain a water-soluble acid sludge as claimed in claim 2, the step of neutralizing the said acid sludge with sodium carbonate, thereby converting the said sludge into a thin, clear, aqueous solution suitable for disposal.

JOSEPH H. WELLS. PHILIP J. WILSON, JR. 

